Every time we think we have the secret to a good cup of coffee, somebody moves the bar. First we traded our robusta for arabica. Then we started grinding our own beans. Now vendors are forcing the next question: glass or thermal?

Experts say the standard drip coffee maker - with a glass pot sitting on a burner - can leave coffee with an acrid taste if it sits on the heat for too long. That's led to an expanding market for machines that drip directly into a stainless-steel carafe, retaining heat without using a warming plate. Manufacturer Capresso has been phasing out glass-pot makers; of its current models, one is glass while six are thermal.

Read more about the thermal coffee makers at azcentral.com.